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LIKELY EFFECTIVE

• Dyslipidemia. Niacin prescription products, in doses of 500 mg or greater, are FDA-approved for primary hyperlipidemia and mixed dyslipidemia. Niacin dietary supplements are generally available in lower doses and have not been shown to improve lipid levels. Details: Prescription niacin is not routinely recommended as second-line therapy for patients who primarily need to decrease low-density lipoprotein (LDL) cholesterol. This is due to results from clinical trials showing no effect on cardiovascular related events or mortality (93346,93354,96208,96211,97308,97477,97336). However, niacin might be considered for patients with mixed hyperlipidemia or patients who need to increase high-density lipoprotein (HDL) cholesterol and lower triglycerides. Niacin might also be effective for isolated hypoalphalipoproteinemia (4817). The most pronounced increases in HDL and decreases in triglycerides occur at 1-1.5 grams daily, and the greatest LDL reduction occurs at 2-3 grams daily. Niacin reduces LDL cholesterol by up to 25%, compared with up to a 55% reduction with statins. High-dose niacin can also decrease triglycerides by 20% to 50%, increase HDL by 13% to 35%, decrease apolipoprotein B levels by 2% to 20%, and decrease lipoprotein(a) levels by 23% (4818,4886,4887,4888,4889,4890,12033,25567,93347,96213). The effects of higher dose extended-release niacin on LDL cholesterol and triglycerides appear to be greater in females than males (25565). Experts recommend maximizing statins first because they have the best evidence for improving cardiovascular outcomes (97477,97336,97337). However, if patients cannot reach their LDL goal with a statin alone or if they cannot tolerate a statin, niacin might be combined with other cholesterol-lowering drugs when diet and single-drug therapy are not adequately effective (8545,25566,93351,94191,97337). Adding low-dose niacin, 50 mg daily, to statin therapy has no additional benefit on lipid levels (8546). Population research in adults without dyslipidemia has also found that higher dietary intake of niacin for 3-10 years is associated with a 29% lower risk of developing dyslipidemia when compared with low dietary niacin intake (110493).
• Pellagra. Oral niacin is FDA-approved for the prevention and treatment of pellagra. Details: Population research has found that low consumption of niacin is associated with an increased risk of developing pellagra (25903). Taking niacin 500-1000 mg daily can resolve symptoms of pellagra within a week of treatment initiation (25904). However, niacinamide is sometimes preferred for this indication because it lacks the vasodilating effects of niacin (15,6243).

POSSIBLY EFFECTIVE

• HIV/AIDS-related dyslipidemia. Oral niacin seems to improve lipid levels in patients with dyslipidemia due to HIV/AIDs. Details: Small clinical trials in HIV patients with dyslipidemia associated with antiretroviral therapy shows that taking extended-release niacin (Niaspan, Abbott Laboratories) titrated up to 2 grams daily for 14-48 weeks improves total cholesterol, high-density lipoprotein (HDL) cholesterol, and triglyceride levels when compared to baseline (25570,25902). Other preliminary clinical research in this population shows that taking extended-release niacin (Niaspan, Abbott Laboratories) titrated to 2 grams daily for up to 2 years improves HDL cholesterol levels, but not total cholesterol or triglyceride levels, when compared with no treatment (25569).
• Metabolic syndrome. Oral niacin seems to improve lipid levels in patients with metabolic syndrome. Details: Clinical research shows that taking niacin (Niaspan, Abbott Laboratories) 2 grams daily orally for 16 weeks reduces triglyceride levels by 39 mg/dL and increases high-density lipoprotein (HDL) cholesterol by 5 mg/dL when compared to baseline in patients with metabolic syndrome. These improvements are significant when compared with placebo and are further increased when niacin is taken along with prescription omega-3 ethyl esters (Lovaza, GlaxoSmithKline Pharmaceuticals) 4 grams daily orally (93353). However, niacin does not seem to improve postprandial glucose levels in patients with metabolic syndrome (97333).

INEFFECTIVE

• Cardiovascular disease (CVD). Oral niacin does not seem to reduce cardiovascular-related events in patients with or without CVD. Details: Overall, niacin is not recommended for primary or secondary prevention of CVD. Most clinical trials and meta-analyses conducted prior to 2011 showed a reduction in cardiovascular-related events, cardiovascular-related mortality, and all-cause mortality in patients taking niacin alone or in combination with a statin or clofibrate for primary or secondary prevention of CVD (4847,7388,25095,25911,25912,93349). However, recent meta-analyses of these studies and additional moderate-to-high quality research conducted in over 39,000 patients show no effect of niacin on cardiovascular-related events, cardiovascular-related mortality, or overall mortality (93346,93354,96208,96211,97308). Additionally, one meta-analysis shows that patients taking niacin are twice as likely to report side effects when compared with placebo (96211).

INSUFFICIENT RELIABLE EVIDENCE to RATE

• Alzheimer disease. It is unclear if oral niacin is beneficial for reducing Alzheimer disease risk. Details: Observational research has found that consuming higher amounts of niacin (17-45 mg daily) from food and supplements is associated with a slower cognitive decline and a lower risk of developing Alzheimer disease when compared with people who consume less niacin (14 mg daily) (12077). It is not known if the risk of Alzheimer disease is reduced by taking a stand-alone niacin supplement.
• Atherosclerosis. It is unclear if oral niacin prevents atherosclerosis progression. Details: Preliminary clinical studies show that taking niacin orally, in combination with colestipol for up to 2 years, might modestly reduce progression of atherosclerosis as measured by coronary lesions and carotid arterial intima-media thickness in high-risk males with existing coronary atherosclerosis (25906,25909,25910). However, niacin does not seem to be better than statins. One clinical study in adults with atherosclerosis and peripheral arterial disease shows that taking extended-release niacin 1500 mg, simvastatin 40 mg, and ezetimibe 10 mg daily for 2 years does not reduce atherosclerosis of the superficial femoral artery when compared with simvastatin alone (96208). Niacin has also not been shown to prevent cardiovascular events or mortality (93346,93354,96208,96211,97308).
• Athletic performance. It is unclear if oral niacin improves athletic performance. Details: Preliminary clinical research in untrained adult males shows that taking niacin 1000 mg orally once before a cycling test does not improve power, respiratory exchange ratio, or time to exhaustion when compared with placebo. In addition, these measures were significantly worse when compared with taking caffeine 5 mg/kg orally as a single dose (107942). Clinical research in untrained males also shows that taking a supplement containing niacin 40 mg, caffeine 400 mg, capsicum extract 66.7 mg, and black pepper extract 10 mg prior to exercising does not improve strength, time to exhaustion, or maximal oxygen consumption when compared with placebo (37873).
• Attention deficit-hyperactivity disorder (ADHD). Although there is interest in using oral niacin for ADHD, there is insufficient reliable information about the clinical effects of niacin for this condition.
• Cancer. It is unclear if dietary niacin is beneficial for cancer. Details: Population research in adults with cancer has found that high dietary niacin intake is associated with 49% and 27% lower risk of cancer-related mortality and all-cause mortality when compared with low dietary niacin intake. The same study also found that taking niacin supplements is associated with a lower risk of cancer-related mortality, but not all-cause mortality when compared with not taking niacin supplements (110496).
• Cataracts. It is unclear if oral niacin is beneficial for preventing cataracts. Details: Population research has found that high dietary intake of niacin is associated with a reduced risk of nuclear cataracts (6378). However, there is no reliable evidence that niacin supplements reduce the risk of cataracts.
• Cholera. It is unclear if oral niacin is beneficial for cholera. Details: One small clinical study in adults with severe cholera shows that taking 1-2 grams niacin orally reduces fluid loss in the stool by 31% to 47% in the first 16 hours when compared with control. The 2 gram dose seemed to result in a greater reduction in fluid loss than the 1 gram dose (4868).
• Erectile dysfunction (ED). It is unclear if oral niacin is beneficial in patients with ED and dyslipidemia. Details: Clinical research in patients with erectile dysfunction and dyslipidemia shows that taking extended-release niacin (Niaspan, Abbott Laboratories) titrated to 1.5 grams nightly for a total of 12 weeks significantly improves penetration frequency and the maintenance of an erection after penetration when compared to baseline (25913). The validity of this finding is limited by the lack of a comparator group.
• Glaucoma. It is unclear if oral niacin is beneficial for preventing or treating glaucoma. Details: Population research has found that higher dietary intake of niacin is associated with a lower odds of having glaucoma. However, this association was not consistently present when adjusting for confounders. The effects of niacin supplementation on glaucoma have not been evaluated (107942).
• Hyperphosphatemia. It is unclear if oral niacin is beneficial for preventing high levels of phosphorus in the blood. Details: Preliminary clinical research in patients on maintenance dialysis who are no longer using phosphate binders shows that taking niacin 375-750 mg daily for 8 weeks reduces serum phosphorus levels by 2.1 mg/dL, increases calcium levels by 0.4 mg/dL, and decreases serum alkaline phosphatase when compared with baseline (25914). However, clinical research in hemodialysis patients with inadequate phosphate control despite using standard phosphate-binding therapy shows that taking niacin at the maximum tolerated dose, up to 1000 mg daily, for 12 weeks, does not decrease serum phosphate levels when compared with placebo (93341). It is possible that this latter study was too small to observe between-group differences in changes in serum phosphate levels.
• Hypertension. It is unclear if dietary niacin is beneficial for preventing hypertension. Details: Observational research in Chinese adults found a J-shaped association between dietary niacin intake and development of hypertension, with the lowest risk occurring in those with a daily dietary niacin intake of 14.3-16.7 mg (104934).
• Meniere disease. Although there is interest in using oral niacin for Meniere disease, there is insufficient reliable information about the clinical effects of niacin for this condition.
• Migraine headache. It is unclear if dietary niacin is beneficial for preventing migraine headaches. Details: Population research in adults has found that high dietary intake of niacin is associated with a 28% lower likelihood of having migraine headaches when compared with low dietary intake of niacin (110495). However, the effect of niacin supplementation on migraines has not been studied.
• Motion sickness. Although there is interest in using oral niacin for motion sickness, there is insufficient reliable information about the clinical effects of niacin for this purpose.
• Parkinson disease. It is unclear if oral niacin is beneficial for improving Parkinson disease symptoms. Details: Low-quality clinical research in adults with Parkinson disease shows that taking slow-release niacin 250 mg orally daily for 12 months improves Parkinson disease motor scores and fatigue scores by 17% and 26%, respectively, when compared with baseline (107944). However, higher quality clinical research shows that taking niacin 250 mg orally daily for 6 months does not improve Parkinson disease motor scores when compared with placebo (107943).
• Retinal vein occlusion. It is unclear if oral niacin is beneficial for improving retinal vein occlusion symptoms. Details: A small case series in patients with chronic retinal vein occlusion shows that taking niacin titrated to 500 mg three times daily for 1 year is associated with reduced central macular thickness and improved visual acuity in over 50% of patients when compared with a control group. The addition of prednisolone eye drops does not alter the outcomes of those taking niacin (96212). The validity of this finding is limited due to the retrospective nature of this study.
• Sickle cell disease. It is unclear if oral niacin is beneficial for improving lipid levels in patients with sickle cell disease. Details: A small clinical study in patients with sickle cell disease shows that taking extended-release niacin titrated to 1.5 grams daily for 12 weeks does not improve vascular function or increase high-density lipoprotein (HDL) or apolipoprotein A-I cholesterol levels when compared with placebo (96209).
• Schizophrenia. Although there is interest in using oral niacin for schizophrenia, there is insufficient reliable information about the clinical effects of niacin for this condition.
• Vertigo. Although there is interest in using oral niacin for vertigo, there is insufficient reliable information about the clinical effects of niacin for this condition. More evidence is needed to rate niacin for these uses.

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LIKELY EFFECTIVE

• Pellagra. Oral niacinamide is approved for the treatment of pellagra and niacin deficiency. Details: Niacinamide is FDA-approved for the prevention and treatment of niacin deficiency and pellagra. Niacinamide is sometimes preferred over niacin for this indication because it lacks the vasodilating and flushing effects of niacin (15,6243).

POSSIBLY EFFECTIVE

• Acne. Topical niacinamide seems to improve acne symptoms in some patients. Oral niacinamide has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: One clinical study shows that applying niacinamide 4% gel twice daily for 8 weeks is as effective as clindamycin 1% gel for reducing the number and severity of acne lesions. The niacinamide gel appears to be more effective in patients with oily skin than those with non-oily skin (93360). Other preliminary clinical research in adults with mild to moderate acne vulgaris shows that applying niacinamide 5% cream twice daily, 10 minutes after applying benzoyl peroxide 2.5% gel, for 12 weeks reduces the number of acne lesions, but not erythema or inflammation, when compared with benzoyl peroxide alone (107711). Niacinamide has also been studied in combination with other ingredients. In preliminary clinical research, oral niacinamide has been reported to improve acne when used in combination with zinc, copper, and folic acid (Nicomide) (25557), or in combination with azelaic acid, zinc, pyridoxine, copper, and folic acid (NicAzel, Elorac Inc.) (90800). In a small observational study, topical niacinamide 4% combined with gallic acid 1% and lauric acid 1% was associated with some improvement in acne (104931). It is unclear if the effects in these studies are due to niacinamide, other ingredients, or the combinations.
• Diabetes. Oral niacinamide does not seem to prevent the onset of type 1 diabetes, although it might slow its progression. Details: Although some older research has suggested that taking high-dose niacinamide can reduce the risk of type 1 diabetes in high-risk children (4874), results from higher quality, more rigorous clinical trials show that taking niacinamide up to 3 grams daily for 5 years does not prevent the onset of type 1 diabetes in first-degree relatives of patients with type 1 diabetes (4875,25553,25554). However, taking niacinamide 1.2 grams/m2 daily for 5 years may prevent the loss of beta-cell function in these patients (25555). Also, there is evidence showing that niacinamide can preserve residual beta-cell function in patients with newly diagnosed type 1 diabetes (4877,4878,4879,4880,25556). Clinical trials, including one placebo-controlled trial and one vitamin E-comparison study, show niacinamide can prolong the "honeymoon period" in those newly diagnosed with type 1 diabetes, when the pancreas is still capable of producing some insulin (4877,4878,4879,4880,25556). However, some scientists have raised concerns about potential induction of insulin resistance with short-term use of niacinamide 2 grams daily for 2 weeks (4881). Niacinamide has also been evaluated in adults with type 2 diabetes. A small clinical study in lean patients with type 2 diabetes who failed sulfonylurea therapy shows that taking niacinamide 500 mg three times daily for 6 months in addition to continuing insulin or a sulfonylurea increases C-peptide release and improves insulin secretion when compared with insulin alone (4882).
• Hyperphosphatemia. Adding oral niacinamide to standard treatment with phosphate binders further lowers blood levels of phosphorus in patients on hemodialysis. Details: A meta-analysis of nine small clinical trials in patients on hemodialysis with hyperphosphatemia who are using a phosphate binder shows that taking niacinamide 250-1500 mg daily for 2-6 months lowers serum phosphorus and parathyroid hormone levels when compared with placebo (98940) Another meta-analysis of two small clinical trials in the same patient population also shows that taking niacinamide, titrated from 500 mg to 1500 mg daily over 8 weeks, reduces serum phosphorus levels by about 0.9 mg/dL when compared with placebo (94188). Other clinical research in this population shows that taking modified-release niacinamide 250-1500 mg orally daily for 12-24 weeks also lowers serum phosphate and parathyroid levels when compared with placebo. However, these effects were not maintained at 40-52 weeks follow-up (107709,110499). In addition, this product was not compared with immediate-release niacinamide. Niacinamide has also been studied in place of phosphate binders. One small clinical study in patients on hemodialysis with hyperphosphatemia shows that taking niacinamide 500-1750 mg daily for 12 weeks, beginning 2 weeks after discontinuation of phosphate binders, decreases serum phosphorus levels by 1.5 mg/dL and intact parathyroid hormone levels by 50 pg/mL, without affecting calcium levels, when compared to baseline (25561).The validity of these findings is limited due to the lack of a control group.
• Nonmelanoma skin cancer. Oral niacinamide might reduce the rate of nonmelanoma skin cancer development. Details: One clinical study in patients with a history of nonmelanoma skin cancers shows that taking niacinamide 500 mg orally twice daily for 12 months reduces the rate of new nonmelanoma skin cancers at 12 months by 23% and the number of actinic keratoses by 13% when compared with placebo (93362). Other clinical research shows that taking niacinamide (Nature's Own, Virginia) 500 mg orally once or twice daily for 4 months reduces the total number of actinic keratoses by up to 35% and decreases the odds of developing at least one nonmelanoma skin cancer by 86% when compared with placebo in patients with at least four actinic keratoses (93365). However, some conflicting research exists. One small clinical study in adults with actinic keratoses shows that taking niacinamide 500 mg twice daily for 120 days does not reduce the number of actinic keratoses when compared with control. However, the validity of this study is limited by the short study duration (107714). A meta-analysis of many small clinical trials shows that using niacinamide, up to 2000 mg orally or 4% topically, daily for 1 month to 5 years lowers the risk of skin cancer, including basal cell carcinoma and cutaneous squamous cell carcinoma by 50% when compared with control. Using niacinamide did not reduce the risk of actinic keratoses. However, the validity of this study is limited by inclusion of populations with different cancer risks and high heterogeneity (110497).
• Osteoarthritis. Oral high-dose niacinamide might be beneficial for improving osteoarthritis symptoms. Details: Clinical research in patients with osteoarthritis shows that taking niacinamide 3 grams daily in six divided doses for 12 weeks improves joint flexibility, reduces inflammation, and modestly decreases use of nonsteroidal anti-inflammatory drugs (NSAIDs) when compared with placebo (4883).

POSSIBLY INEFFECTIVE

• Brain tumor. Adding high-dose oral niacinamide to chemotherapy does not seem to improve survival in patients with brain tumors. Details: Preliminary clinical research in patients with surgically resected brain tumors shows that treatment with radiotherapy, niacinamide, and carbogen does not improve survival when compared with radiotherapy alone or radiotherapy plus carbogen (11695,11696).

INSUFFICIENT RELIABLE EVIDENCE to RATE

• Age-related cognitive decline. Although there is interest in using oral niacinamide for age-related cognitive decline, there is insufficient reliable information about the clinical effects of niacinamide for this purpose.
• Age-related macular degeneration (AMD). Oral niacinamide has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: One small clinical study in patients with early-stage age-related maculopathy shows that taking a combination of niacinamide 18 mg, vitamin E 20 mg, and lutein 15 mg daily for nearly a year improves retinal function when compared with no treatment (60134). It is unclear if this effect is due to niacinamide, other ingredients, or the combination.
• Aging skin. It is unclear if topical niacinamide improves symptoms of aging skin. Details: A small study in females with signs of facial photo-aging shows that applying niacinamide 5% cream to half of the face twice daily for 12 weeks improves blotchiness, the appearance of wrinkles, skin elasticity, and skin pigmentation when compared with applying placebo cream to the other half of the face (25551).
• Atopic dermatitis (eczema). It is unclear if topical niacinamide improves eczema symptoms. Details: A small clinical study in patients with atopic dermatitis and dry skin shows that applying niacinamide 2% cream twice daily for 8 weeks decreases skin water loss and improves skin hydration when compared with using a white petrolatum moisturizer (25560).
• Attention deficit-hyperactivity disorder (ADHD). Oral niacinamide has only been evaluated in combination with other vitamins; its effect when used alone is unclear. Details: A small clinical study in children with ADHD shows that taking a maximum of niacinamide 3 grams, ascorbic acid 3 grams, calcium pantothenate 1.2 grams, and pyridoxine 600 mg daily for 3 months seems to improve behavior in 29% of participants when compared with baseline (9957). The validity of this finding is limited by the lack of a comparator group.
• Bladder cancer. Oral niacinamide has only been evaluated in combination with carbogen for improving survival in advanced bladder cancer; its effect when used alone is unclear. Details: A phase II clinical study in patients with locally advanced bladder cancer shows that adding inhaled carbogen and oral niacinamide 40-60 mg/kg about 2 hours before radiotherapy shows a trend to improved survival at 3 years when compared with inhaled carbogen and radiotherapy (25558), and a larger phase III study shows that carbogen and oral niacinamide improves 3-year survival by about 13% when compared with radiotherapy alone (93366). An observational follow-up of the phase III study found a trend to increased survival at 5 years in the carbogen and niacinamide group when compared with radiotherapy alone. And in a subgroup of patients with tumor necrosis, the 5-year survival was significantly greater with carbogen and niacinamide when compared with radiotherapy alone (93356). It is unclear if these effects are due to niacinamide, carbogen, or the combination.
• Child growth. It is unclear if oral niacinamide improves child growth. Details: Preliminary clinical research in children in rural Tanzania shows that supplementing niacinamide orally from birth to 18 months of age does not improve length-for-age, weight-for-age, or head circumference when compared with control. Niacinamide was initially supplemented to breast-feeding mothers, 250 mg daily, until 6 months of age, followed by 100 mg daily taken by the child until 18 months of age (107713).
• Coronavirus disease 2019 (COVID-19). It is unclear if oral niacinamide is beneficial for COVID-19. Details: Observational research in adults with acute kidney injury secondary to coronavirus disease-19 infection has found that taking niacinamide 1000 mg orally daily for 7 days is associated with a 55% lower risk of mortality when compared with control. However, taking niacinamide was not associated with a lower risk of renal replacement therapy (110500).
• Cutaneous lupus erythematosus (CLE). It is unclear if topical niacinamide is beneficial for CLE. Details: Preliminary clinical research in adults with discoid lupus erythematosus, a type of CLE, shows that applying topical niacinamide 2% to 4% twice daily for 12 weeks modestly improves lesion scores, but not quality of life scores, when compared with placebo. However, the study may have been inadequately powered to detect a difference between groups (110498).
• Depression. Although there is interest in using oral niacinamide for depression, there is insufficient reliable information about the clinical effects of niacinamide for this condition.
• Diabetic neuropathy. Oral niacinamide has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Preliminary clinical research in adults with diabetic polyneuropathy shows that taking a specific combination product (Cytoflavin, Polysan) containing niacinamide, inosine, riboflavin, and succinate daily for 12 weeks improves symptom scores, including paresthesia and numbness scores, when compared with placebo. The therapy was administered intravenously, containing niacinamide 20 mg, inosine 40 mg, riboflavin 4 mg, and succinate 200 mg, for 10 days followed by orally, containing niacinamide 50 mg, inosine 100 mg, riboflavin 10 mg and succinate 600 mg, for the remainder of the study (110503).
• Erythema. Topical niacinamide has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: There is interest in using niacinamide to reduce the side effects of topical tretinoin, including erythema. A small preliminary clinical study in patients using isotretinoin for acne shows that applying a specific cream (Sebiaclear Hydra, SVr Laboratoire Dermatologique) containing niacinamide 5% and omega-ceramides 8% twice daily for 6 months reduces isotretinoin-induced erythema, dryness, and itching of the skin when compared with a glycerin placebo (98938). It is not clear if this effect is due to niacinamide, omega-ceramides, or the combination.
• Head and neck cancer. Oral niacinamide has only been evaluated in combination with carbogen for improving survival in laryngeal cancer; its effect when used alone is unclear. Details: A phase III clinical trial in patients with laryngeal cancer shows that treatment with accelerated radiotherapy plus carbogen and niacinamide 60 mg/kg taken orally 1-1.5 hours prior to each fraction of radiation improves local tumor control, but does not improve overall survival or 5-year disease-free survival, when compared with accelerated radiotherapy alone. In a subgroup of patients with hypoxic tumors, anemia, or high expression of epidermal growth factor receptor, receiving niacinamide and carbogen seems to improve both survival and tumor control when compared with radiotherapy alone (93358,93359,93363).
• Melasma. It is unclear if topical niacinamide improves uneven skin pigmentation. Details: A small clinical study in Japanese females with uneven facial hyperpigmentation shows that applying niacinamide 5% moisturizer to the face twice daily reduces hyperpigmentation and increases skin lightness after 4 weeks when compared with placebo moisturizer. However, further improvements are not observed after another 4 weeks of treatment (25552). Another small clinical study in Korean females with uneven facial hyperpigmentation shows that applying a moisturizer containing niacinamide 2% plus tranexamic acid 2% (Regederm RX White Project, Aestura) twice daily for 8 weeks reduces skin pigmentation by about 9% when compared with a placebo cream (93361).
• Non-Hodgkin lymphoma. It is unclear if adding oral niacinamide to chemotherapy reduces relapses of refractory lymphoma. Details: One small clinical study in patients with relapsed or refractory lymphoma shows that 24% of patients achieve complete or partial remission and 57% achieve disease stabilization when compared with baseline, following treatment with vorinostat 400 mg daily and niacinamide titrated from 20 mg/kg to 100 mg/kg over the first 14 days of a 21-day cycle for up to 18 cycles (93355). It is unclear how these outcomes compare to using vorinostat alone, or to other control treatments.
• Nonalcoholic fatty liver disease (NAFLD). It is unclear if oral niacinamide is beneficial for NAFLD. Details: Preliminary clinical research in adults with NAFLD and diabetes shows that taking a specific niacinamide product (Nature's Life) 1000 mg orally daily for 12 weeks does not improve liver function tests, liver steatosis, or liver fibrosis when compared with no intervention. However, some quality of life domain scores were moderately improved. However, the study may have been inadequately powered to detect a difference between groups (110502).
• Premenstrual syndrome (PMS). Although there is interest in using oral niacinamide for PMS, there is insufficient reliable information about the clinical effects of niacinamide for this condition.
• Pruritus. It is unclear if oral niacinamide reduces pruritus in patients with kidney failure. Details: A small clinical study in patients with pruritus due to kidney failure shows that taking niacinamide sodium 500 mg twice daily for 4 weeks does not reduce pruritus severity when compared with placebo (93364). This study is limited due to small size and short study duration.
• Psoriasis. It is unclear if oral niacinamide is beneficial for psoriasis. Details: Preliminary clinical research in adults with mild to moderate psoriasis shows that applying niacinamide 4% cream topically twice daily for 12 weeks improves psoriasis scores by 31% when compared with baseline. The validity of these results is limited by the lack of a comparator group (110501).
• Rosacea. Oral niacinamide has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Preliminary clinical research shows that 71% of adult and adolescent patients with rosacea who take a combination product (Nicomide) containing niacinamide 750 mg, zinc 25 mg, copper 1.5 mg, and folic acid 500 mcg once or twice daily report improvement in appearance after 4 weeks when compared to baseline (25557). The validity of these findings is limited by the lack of a control group.
• Schizophrenia. Although there is interest in using oral niacinamide for schizophrenia, there is insufficient reliable information about the clinical effects of niacinamide for this condition.
• Seborrheic dermatitis. It is unclear if topical niacinamide is beneficial for reducing seborrheic dermatitis symptoms. Details: One small clinical study in patients with seborrheic dermatitis shows that applying niacinamide 4% cream once daily for 12 weeks reduces the severity of symptoms such as redness and scaling by 75%, compared with a 35% reduction when using a placebo cream (93357). More evidence is needed to rate niacinamide for these uses.

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EFFECTIVE

• Pyridoxine-dependent epilepsy. Intravenous vitamin B6 is effective for controlling pyridoxine-dependent seizures. Details: Pyridoxine-dependent seizures are a rare type of refractory seizures in neonates that do not respond to anticonvulsant drugs. These seizures are typically controlled within minutes of intravenous administration of pyridoxine, a form of vitamin B6. Pyridoxine-dependent seizures can be due to genetic (autosomal recessive) pyridoxine dependency, or more commonly, a result of the use of high-dose pyridoxine during pregnancy (8197,8198).
• Sideroblastic anemia. Oral vitamin B6 is effective for treating hereditary sideroblastic anemia. Details: Taking vitamin B6 (pyridoxine) orally is effective for treating hereditary sideroblastic anemia (15,9518). Taking the active form of vitamin B6 (pyridoxal-5'-phosphate) also seems to be effective in cases in which the patient does not respond to pyridoxine (93049).
• Vitamin B6 deficiency. Oral vitamin B6 is effective for preventing and treating vitamin B6 deficiency. Details: Taking oral vitamin B6 can prevent and treat vitamin B6 deficiency (15).

LIKELY EFFECTIVE

• Hyperhomocysteinemia. Taking vitamin B6 orally, alone or in combination with folic acid, is effective for reducing hyperhomocysteinemia. Details: Vitamin B6 (pyridoxine) seems to lower homocysteine concentrations when folic acid and vitamin B12 are at physiologic levels or when given with folic acid and vitamin B12 supplements (9451,83042,107136). A combination of vitamin B6 100 mg and folic acid 0.5 mg daily seems to lower homocysteine levels by about 35% and is recommended for people with postprandial hyperhomocysteinemia (1489,9406). Other research shows that taking pyridoxine 50-200 mg daily reduces postprandial homocysteine levels by 32% to 35% (9406,10350). Pyridoxine also seems to reduce homocysteine levels in patients with kidney failure, kidney transplant patients (1489,6884,9414,9415), or patients who receive general anesthesia with nitrous oxide (9481). However, some research in healthy adults suggests that adding pyridoxine to folic acid might not provide any additional benefit over folic acid alone (9400,9405,9409,50145). Hyperhomocysteinemia is considered by some to be an independent risk factor for atherosclerosis, recurrent thromboembolism, deep vein thrombosis, myocardial infarction, and ischemic stroke (1899,3323,9402,9405,9408,9409). However, elevated homocysteine levels may be a marker, as opposed to a cause, of vascular disease (11387,11388). A 5 µmol/L increase in plasma homocysteine increases the risk of cerebrovascular disease by 50% and the odds of coronary heart disease by 60% and 80% in males and females, respectively (9407,9411). However, it is not clear if reducing homocysteine levels results in reduced cardiovascular morbidity and mortality (1489,6883,6884,9308,9400,9405,9409). Folic acid, vitamin B6, and vitamin B12 supplementation can reduce total homocysteine from 13.4 to 11 µmol/L. However, this reduction does not seem to help with secondary prevention of death or myocardial infarction, and some research even suggests an increase in cardiovascular disease (CVD) risk (11387,13482,50423,83050,97619). There is also debate about whether supplementation with homocysteine-lowering B vitamins can reduce the risk of stroke. A number of large clinical studies and meta-analyses show that supplementation with folic acid, vitamin B6, and vitamin B12, alone or in combination, does not reduce the risk of stroke in patients with CVD or impaired renal function (11387,13482,50423,83050,96150). However, a more recent meta-analysis shows that B vitamin supplementation modestly reduces the relative risk of stroke by 10% when compared with placebo in patients at risk for or with a history of CVD (97619). Also, a meta-analysis in patients with a history of stroke shows that B vitamin supplementation modestly reduces the relative risk of stroke recurrence by 13% and the risk of vascular death by 11% when compared with placebo (107136).

POSSIBLY EFFECTIVE

• Antipsychotic-induced hyperprolactinemia. It is unclear if oral vitamin B6 is beneficial for patients with antipsychotic-induced hyperprolactinemia. Details: Clinical research in male patients with hyperprolactinemia who are on a consistent antipsychotic dose shows that taking vitamin B6 300 mg twice daily for 16 weeks reduces serum prolactin levels by 68%, compared with 37% in patients taking aripiprazole 5 mg twice daily. Also, 67% of patients taking vitamin B6 had prolactin levels less than 40 mcg/mL versus 2% of those taking aripiprazole (107128).
• Kidney stones (nephrolithiasis). Oral vitamin B6 seems to decrease urinary oxalate levels and decrease the risk of kidney stone formation in some patients. Details: There is some evidence that taking vitamin B6 (pyridoxine) orally, alone or in combination with magnesium, can decrease urinary oxalate levels in people with type I primary hyperoxaluria, a hereditary disorder (1201,6437,6438,6439,6440,8548,8549,8550). Additionally, a small clinical study in this population suggests that intravenous pyridoxine hydrochloride can reduce urinary oxalate by 25.5% when compared to baseline (90796). In patients with idiopathic hyperoxaluria, taking a combination of pyridoxine 25mg and magnesium oxide 400 mg for 3 months decreases urinary oxalate by approximately 16%, with 68% of patients experiencing a reduction. However, supplementation is less effective than following a low-oxalate diet, which reduces urinary oxalate in 91% of patients by an average of 31% (107127). There is also preliminary evidence that higher pyridoxine intake in females with no history of kidney stones is associated with decreased risk of kidney stone formation (6441), but this association has not been found in males (6442).
• Pregnancy-induced nausea and vomiting. Oral vitamin B6 may reduce nausea and vomiting in some pregnant patients and is sometimes used in combination with doxylamine. Details: While some conflicting evidence exists, most small clinical studies suggest that oral vitamin B6 is effective for improving nausea and vomiting associated with pregnancy when compared with baseline or placebo. However, vitamin B6 may not be as effective as ginger (110459). Two small clinical studies show that taking vitamin B6 (pyridoxine) 25 mg every 8 hours for 3-4 days decreases pregnancy-induced nausea severity and vomiting incidence when compared with placebo (6168,16306). A larger clinical trial shows that taking lower doses of vitamin B6, 10 mg every 8 hours over 5 days, improves pregnancy-induced nausea, but not vomiting, when compared with placebo (6167). A small clinical study in patients with mild to moderate nausea and vomiting shows that taking a higher dose of 40 mg twice daily for 4 days is more effective than placebo, but no better than ginger 500 mg twice daily (99404). The American College of Obstetrics and Gynecology (ACOG) considers vitamin B6 at a dose of 10-25 mg 3 to 4 times daily a first-line treatment for pregnancy-induced nausea and vomiting due to its benign safety profile (111601). However, it is not effective for all patients, such as those with hyperemesis gravidarum, a severe form of pregnancy-induced nausea and vomiting. Adding vitamin B6 20 mg three times daily for 2 weeks to intravenous rehydration, metoclopramide, and thiamine seems to be no more effective than placebo for reducing vomiting in hyperemesis gravidarum (99405). Vitamin B6 is also sometimes used in combination with doxylamine. In fact, a combination of vitamin B6 plus doxylamine (Diclegis or Bonjesta, Duchesnay Inc., and various generics) has been approved by the US Food and Drug Administration (FDA) as a prescription product111601). ACOG recommends vitamin B6 in combination with doxylamine as another first-line treatment option (111601). However, the clinical trial used to obtain FDA approval has some methodological problems, and the significance of the results has been questioned. The improvement in symptom scores seen with Diclegis was less than one point on a 13-point scale, which is unlikely to be clinically significant (97998). Also, some clinical research shows that taking pyridoxine 25 mg and doxylamine 12.5 mg is less effective than ondansetron 4 mg when taken every 8 hours for 5 days. Only 41% of the patients using pyridoxine and doxylamine had a clinically significant reduction in nausea, compared to 92% of patients using ondansetron (90797). The combination of vitamin B6 and doxylamine is also studied with acupuncture. A large clinical study in patients with moderate to severe pregnancy-induced nausea and vomiting conducted in China shows that taking vitamin B6-doxylamine (Diclegis, Duchesnay, Inc) 20 to 40 mg each at bedtime for 14 days in combination with daily acupuncture modestly improves patient-reported nausea and vomiting scores when compared with either intervention alone (111820). However, it is unclear whether this improvement is clinically significant.
• Premenstrual syndrome (PMS). Oral vitamin B6 seems to reduce PMS symptoms. Details: There is some evidence that taking vitamin B6 (pyridoxine) orally can improve symptoms of PMS such as breast pain or tenderness (mastalgia) and depression in some patients. Pyridoxine in doses of at least 50 mg daily, plus magnesium oxide 200 mg daily, seems to relieve PMS-related anxiety and other symptoms (8555,39007,82962). Although some clinicians advocate doses of pyridoxine 200-500 mg daily for PMS, doses of 50-100 mg daily seem to work just as well. There is no apparent dose-response curve for PMS, so the lowest effective dose should be used. Higher doses might increase the risk of side effects (3093).

POSSIBLY INEFFECTIVE

• Age-related cognitive decline. Oral vitamin B6 does not seem to slow age-related cognitive decline. Details: One clinical trial in elderly people with memory complaints shows that taking a combination of B vitamins, including folic acid 0.8 mg, vitamin B12 0.5 mg, and vitamin B6 (form not specified) 20 mg daily for 24 months reduces cerebral atrophy in the gray matter regions associated with Alzheimer disease by up to seven-fold when compared with placebo. However, this protection does not occur in patients with the lowest average blood levels of homocysteine (90374). Furthermore, other clinical research shows that taking vitamin B6 (pyridoxine) 3-75 mg daily in combination with folic acid and vitamin B12 does not improve cognitive function in elderly adults (14392,50225,50510).
• Alzheimer disease. Oral vitamin B6 does not seem to improve cognitive function in patients with Alzheimer disease when used in combination with other B vitamins. Also, oral vitamin B6 does not seem to reduce the risk of developing this condition. Details: Clinical research in patients with probable Alzheimer disease taking routine medications shows that taking vitamin B6 25 mg with folic acid 5 mg and vitamin B12 1 mg daily for 18 months does not have a beneficial effect on cognitive function or the severity of disease when compared with placebo. In this study, all patients were consuming a folate-fortified diet (50319). Also, population research in elderly adults has found that a high intake of vitamin B6 from dietary or supplemental sources is not associated with a decreased risk of Alzheimer disease when compared to lower vitamin B6 intake (13165,15270).
• Carpal tunnel syndrome. Oral vitamin B6 does not seem to reduce symptoms of carpal tunnel syndrome. Details: Most research shows that people with carpal tunnel syndrome are not generally deficient in vitamin B6 and do not benefit from taking vitamin B6 supplements (8203,8937,9448,9450,9478,9482). Although early studies by a single group of researchers, as well as anecdotal reports, suggest that taking vitamin B6 may relieve carpal tunnel symptoms, more reliable research has not supported these findings (8202,9445,9447,9449,9483,15955,83086).
• Cataracts. Oral vitamin B6 does not seem to slow cataract development. Details: Clinical research in females with existing cardiovascular disease (CVD) or at increased risk of CVD shows that taking a combination of folic acid 2.5 mg, vitamin B6 (form not specified) 50 mg, and vitamin B12 1 mg daily for an average of 7.3 years does not reduce the risk of cataracts when compared with placebo. Furthermore, the risk of cataract extraction was increased by 28% (96149).
• Chemotherapy-induced acral erythema. While some conflicting evidence exists, most research suggests that oral or topical vitamin B6 does not seem to prevent or reduce the severity of acral erythema induced by chemotherapy. Details: A meta-analysis of 10 clinical trials and 4 observational studies shows that taking vitamin B6 60-500 mg daily for up to 8 chemotherapy cycles does not prevent chemotherapy-induced acral erythema or reduce the incidence of severe cases when compared with control. Most studies used capecitabine chemotherapy alone or in combination, and one study used pegylated liposomal doxorubicin; however, no subgroup analysis was conducted to differentiate chemotherapy regimens. Results did not seem to vary based on study location, study design, or vitamin B6 dose (104930). However, a more recent preliminary clinical study in patients receiving doxorubicin for multiple myeloma shows that taking vitamin B6 100 mg on the first day of chemotherapy then twice daily for 7 days with each cycle reduces the risk of developing acral erythema by 72%, but does not improve the severity of acral erythema, when compared with no vitamin B6 supplementation (110458). Also, one small, low-quality clinical study suggests that taking vitamin B6 400 mg daily reduces the risk of moderate or severe chemotherapy-induced acral erythema when compared with vitamin B6 200 mg daily; however, the higher dose also seems to be associated with worsened tumor response and increased treatment failure (97620). Topical vitamin B6 has also failed to show benefit. A small clinical study in patients with acral erythema from capecitabine or pegylated liposomal doxorubicin shows that applying vitamin B6 1% cream to affected areas three times daily for 6 weeks does not improve symptoms when compared with placebo (104929).
• Colorectal adenoma. Oral vitamin B6 does not seem to reduce the risk of developing colorectal adenomas. Details: Clinical research shows that taking a combination of B vitamins, including folic acid 2.5 mg, vitamin B6 (pyridoxine) 50 mg, and vitamin B12 1 mg, daily for up to 9.2 years does not reduce the risk of colorectal adenoma in females at high risk of cardiovascular disease when compared with placebo (90389).
• Eclampsia. Oral or intramuscular vitamin B6 does not seem to reduce the risk of eclampsia. Details: Meta-analyses of limited clinical research in pregnant patients show that taking vitamin B6 (pyridoxine), either as 25 mg daily or a single dose of 100 mg orally or intramuscularly, does not reduce the risk of eclampsia when compared with control (83046,96166).
• Osteoporosis. Oral vitamin B6 does not seem to reduce the risk of osteoporotic fractures. Details: Clinical research in patients with cerebrovascular disease shows that taking a combination of B vitamins, including folic acid 2 mg, vitamin B6 (form not specified) 25 mg, and vitamin B12 500 mcg daily for up to 10.5 years does not prevent osteoporotic fractures when compared with placebo (90377). Furthermore, a secondary analysis of two large studies in patients with cardiovascular disease has found that taking vitamin B6 (pyridoxine) 40 mg daily in addition to folic acid and vitamin B12 for 1-3 years is associated with a 42% increased risk of hip fracture over an 11-year period when compared with only folic acid and vitamin B12 (96163). This finding is limited because these studies were not designed to assess the effects of vitamin B6 on fracture risk and the analyses were not adjusted for baseline bone health or fall risk.
• Pre-eclampsia. Oral or intramuscular vitamin B6 does not seem to reduce the risk of pre-eclampsia. Details: Meta-analyses of limited clinical research in pregnant patients show that taking vitamin B6 (pyridoxine), either as 25 mg daily or a single dose of 100 mg orally or intramuscularly, does not reduce the risk of pre-eclampsia when compared with placebo (83046,96166).
• Preterm labor. Oral or intramuscular vitamin B6 does not seem to reduce the risk of preterm labor. Details: Meta-analyses of limited clinical research in pregnant patients shows that taking vitamin B6 (pyridoxine), either as 25 mg daily or a single dose of 100 mg orally or intramuscularly, does not reduce the risk of preterm labor when compared with placebo (83046,96166).

INSUFFICIENT RELIABLE EVIDENCE to RATE

• Acne. Oral vitamin B6 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Preliminary clinical research in adults and children with inflammatory acne shows that taking 1-4 tablets of a specific product (NicAzel, Elorac Inc.) containing vitamin B6 (pyridoxine), nicotinamide, azelaic acid, zinc, copper, and folic acid for 8 weeks reduces inflammatory lesions and improves appearance in 88% and 81% of patients, respectively, when compared to baseline (90800). The validity of these findings is limited by the lack of a comparator group.
• Age-related macular degeneration (AMD). Oral vitamin B6 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: A large-scale clinical study shows that taking vitamin B6 (pyridoxine) 50 mg, vitamin B12 1000 mcg, and folic acid 2.5 mg daily reduces the risk for AMD in females over 40 years of age with a history of cardiovascular disease (CVD) or with risk factors for CVD. Those who took this combination for an average of 7.3 years had a 34% reduced risk of developing AMD and a 41% reduced risk of visually significant AMD when compared with placebo (14620). It is unclear if this effect is due to vitamin B6, other ingredients, or the combination.
• Angioplasty. Oral vitamin B6 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Some evidence suggests that vitamin B6 (pyridoxine) 10 mg, folic acid 1 mg, and vitamin B12 400 mcg daily can decrease the rate of restenosis in patients treated with balloon angioplasty (8009,9412). However, this combination does not seem to be as effective for reducing restenosis in patients after coronary stenting (8009). An intravenous loading dose of folic acid, vitamin B6 (pyridoxine), and vitamin B12 followed by oral administration of folic acid 1.2 mcg, vitamin B6 (pyridoxine) 48 mg, and vitamin B12 60 mcg daily after bare metal coronary stenting also does not seem to reduce restenosis and might actually increase restenosis (12150,12151). Due to the lack of evidence of benefit and potential for harm, this combination of vitamins should not be recommended for patients receiving coronary stents (12151). It is unclear if any effects are due to vitamin B6, other ingredients, or the combination.
• Antipsychotic-induced metabolic side effects. It is unclear if oral vitamin B6, as an adjunct to progesterone, is beneficial in patients with antipsychotic-induced amenorrhea. Details: A small clinical study in females with antipsychotic-induced amenorrhea shows that taking vitamin B6 80 mg three times daily for 1 month plus intramuscular progesterone daily for 5 days increases levels of estradiol and follicle stimulating hormone, reduces prolactin levels, and increases the rate of clinical efficacy, defined as the normalization of menstruation and improvement in endocrine indicators, by 14% when compared with progesterone alone (110457).
• Anxiety. It is unclear if oral vitamin B6 is beneficial in patients with anxiety. Details: Clinical research in college students shows that taking vitamin B6 100 mg daily for one month does not reduce anxiety scores when compared with placebo (110453). However, because a diagnosis of anxiety was not a requirement for study participation, it is unclear if these findings can be generalized to patients diagnosed with anxiety.
• Asthma. It is unclear if oral vitamin B6 is beneficial in patients with asthma. Details: Preliminary clinical studies show that taking vitamin B6 (pyridoxine) 200-300 mg daily may improve symptoms of asthma in some patients, but not others, when compared with placebo (7064,7065). Studies have yielded conflicting results, with some research suggesting that it may only be beneficial in children with severe asthma (7065). Additionally, some research suggests that theophylline may lower vitamin B6 levels, although it is unclear if vitamin B6 supplementation is beneficial (4522,7066,9503).
• Atherosclerosis. Oral vitamin B6 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Clinical research in patients with intermediate risk for coronary heart disease shows that taking a specific supplement (Kyolic, Total Heart Health, Formula 108, Wakunga) containing vitamin B6 12.5 mg, aged garlic extract 250 mg, vitamin B12 100 mcg, folic acid 300 mcg, and L-arginine 100 mg daily for 12 months reduces coronary artery calcium progression when compared with placebo (88385). It is unclear if this effect is due to vitamin B6, other ingredients, or the combination.
• Atopic dermatitis (eczema). It is unclear if oral vitamin B6 is beneficial in patients with eczema. Details: A small clinical study in children with eczema shows that taking vitamin B6 (pyridoxine hydrochloride) 50 mg daily for 4 weeks does not reduce symptoms such as redness and itchiness when compared with placebo (83090).
• Attention deficit-hyperactivity disorder (ADHD). It is unclear if oral vitamin B6 is beneficial for ADHD. Details: A small crossover study in children with ADHD shows that taking vitamin B6 600 mg, niacinamide and ascorbic acid 3 grams, and calcium pantothenate 1.2 grams daily for 6 weeks does not improve behavior scores when compared with placebo (9957).
• Autism spectrum disorder. Although there is interest in using oral vitamin B6 for autism, there is insufficient reliable information about the clinical effects of vitamin B6 for this condition.
• Bipolar disorder. It is unclear if oral vitamin B6 is beneficial in patients with bipolar disorder. Details: A small clinical trial in patients with type 1 bipolar disorder who are taking lithium and experiencing an acute episode of mania shows that taking vitamin B6 80 mg daily for 8 weeks does not improve cognitive function or the severity of mania when compared with placebo. Cognitive function was reduced in patients taking vitamin B6; any effect on sleep was unclear (107132).
• Cancer. It is unclear if oral vitamin B6 reduces overall cancer risk. Details: Population research has found that higher dietary intake of vitamin B6 is associated with a 22% reduced risk of cancer, including esophageal, pancreatic, gastric, colorectal, and breast cancer. However, when dietary and supplemental vitamin B6 intake is considered, the inverse association between vitamin B6 and cancer risk is weaker and limited to fewer tumor sites. Furthermore, a meta-analysis of 9 clinical studies shows that taking vitamin B6 3-100 mg orally daily for 2-7.3 years, in combination with vitamin B12 and folate, does not reduce the risk of cancer in patients with cardiovascular disease or kidney failure (96164).
• Cardiovascular disease (CVD). Oral vitamin B6, taken along with other B vitamins, does not seem to improve secondary prevention of death or myocardial infarction in patients with CVD. However, it might slightly lower the risk of stroke. Details: Overall evidence from clinical research and meta-analyses shows that taking vitamin B6 in combination with folic acid and/or vitamin B12 does not seem to help with secondary prevention of death or myocardial infarction in patients with or at risk for CVD (11387,13482,34540,50423,83050,90379,97619). In fact, some research suggests that long-term supplementation with vitamin B6, folic acid, and vitamin B12 for secondary prevention increases the risk of CVD by 20% despite lowering homocysteine levels by 30% (13482). However, some research shows that taking vitamin B6 in combination with other B vitamins modestly reduces the risk of stroke, although results are conflicting (11387,13482,50423,83050,96150,96165,97619,107136). Additionally, it is unclear which specific combination of B vitamins is optimal for reducing stroke risk and which patients are most likely to benefit. In 2001, prior to the publication of the highest quality research on this topic, the US Food and Drug Administration (FDA) approved a qualified health claim stating that, as part of a well-balanced diet that is low in saturated fat and cholesterol, folic acid, vitamin B6, and vitamin B12 may reduce the risk of vascular disease (102368).
• Cognitive function. Oral vitamin B6 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: A moderate-sized clinical study in healthy adults aged 40-65 years shows that taking a supplement containing vitamin B6, ginkgo leaf, bacopa, and other B vitamins twice daily for 12 weeks does not improve memory or attention when compared with placebo (111334).
• Colorectal cancer. It is unclear if oral vitamin B6 reduces the risk of colorectal cancer. Details: A meta-analysis of observational studies suggests that the highest dietary intake of vitamin B6 is associated with a 20% reduced risk of colorectal cancer when compared with the lowest dietary intake. However, this association was not shown in subgroup analyses of studies conducted in Australia, Europe, or North America (111600). The validity of this analysis is limited by the heterogeneity of the included studies.
• Dental caries. There is limited evidence on the oral use of vitamin B6 for dental decay during pregnancy. Details: Meta-analyses of limited clinical research show that taking vitamin B6 (pyridoxine), 25 mg daily or a single dose of 100 mg orally or intramuscularly, may reduce the risk of dental decay during pregnancy when compared with placebo (83046,96166).
• Depression. It is unclear if oral vitamin B6 reduces the risk of developing depression or improves symptoms of depression. Details: Clinical research in healthy college students shows that taking vitamin B6 100 mg daily for one month does not reduce depression scores when compared with placebo (1104453). However, because a diagnosis of depression was not a requirement for study participation, it is unclear if these findings can be generalized to patients diagnosed with depression. Whether vitamin B6 reduces the risk of developing depression is also unclear. A meta-analysis of population research has found that the highest dietary intake of vitamin B6 is associated with a 19% lower risk of depression when compared with the lowest intake. However, sub-analyses suggest that this association is only relevant in females and not males (107133). In one individual population study in community dwelling older adults included in the analysis, the consumption of at least 1.71 mg of vitamin B6 daily from food was associated with a 43% reduction in the likelihood of becoming depressed when compared with the consumption of 1.33 mg or less daily in females. However, there was no association between vitamin B6 levels and risk of depression in males, and the finding in females was no longer significant when adjusted for total energy intake, since foods rich in vitamin B6 are energy-dense (96168). Another observational longitudinal study in healthy adults starting oral contraceptives containing ethinyl estradiol and levonorgestrel has found that taking vitamin B6 25 mg daily for 6-12 months is associated with a 40% lower risk of depression when compared with no supplementation (90789). Most available studies are cross-sectional in nature, making any conclusions related to causation difficult.
• Diabetes. It is unclear if oral vitamin B6 is beneficial in patients with type 2 diabetes or gestational diabetes. Details: Observational research in Chinese adults with type 2 diabetes has found that dietary intake of vitamin B6 in the highest quartile is associated with 53% lower odds of developing cardiovascular disease, defined as a non-fatal myocardial infarction, non-fatal stroke, or hospitalization for unstable angina, when compared with vitamin B6 intake in the lowest quartile (110452). Small clinical studies in patients with gestational diabetes and vitamin B6 deficiency shows that taking vitamin B6 (pyridoxine) 100 mg daily for 2 weeks improves glucose tolerance and blood glucose levels when compared with baseline (82967,83088). However, there is concern that these findings were confounded by dietary alterations. This benefit was not observed in a subsequent small case series in patients with gestational diabetes (22380).
• Diabetic neuropathy. Oral vitamin B6 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Clinical research suggests that taking a combination of B vitamins, including folic acid (L-methylfolate), vitamin B12 (methylcobalamin), and vitamin B6 (pyridoxal-5'-phosphate) for 24 weeks does not improve neural dysfunction based on vibration perception when compared with placebo in patients with diabetic neuropathy. However, taking this combination appears to modestly improve neuropathy symptoms and quality of life related to mental functioning when compared with placebo (90375).
• Dysmenorrhea. It is unclear if oral vitamin B6 is beneficial in patients with dysmenorrhea. Details: Preliminary clinical research shows that taking vitamin B6 (form not specified) 200 mg daily reduces pain associated with dysmenorrhea when compared with placebo. However, taking vitamin B6 in combination with magnesium does not reduce pain when compared with placebo (77388).
• Fibromyalgia. It is unclear if oral vitamin B6 is beneficial in patients with fibromyalgia. Details: A small clinical study in patients with fibromyalgia shows that taking vitamin B6 80 mg daily for 8 weeks does not improve pain, disease severity, anxiety, depression, or quality of life when compared with placebo (110454).
• Gastroenteritis-associated nausea and vomiting. It is unclear if oral vitamin B6 is beneficial in children with gastroenteritis. Details: A small clinical study in children aged 6 months to 12 years with acute viral gastroenteritis shows that taking vitamin B6 (form not specified) does not improve symptoms of dehydration or the frequency of vomiting when compared with placebo (90793).
• Hypertension. It is unclear if oral vitamin B6 reduces blood pressure. Details: One small clinical study in patients with essential hypertension shows that taking vitamin B6 (pyridoxine hydrochloride) 5 mg/kg daily for 4 weeks can reduce systolic and diastolic blood pressure when compared with baseline (83091). The validity of this finding is limited by the lack of a control group.
• Hypertriglyceridemia. It is unclear if oral vitamin B6 reduces triglyceride levels. Details: Preliminary clinical research shows that vitamin B6 (form not specified) 50 mg daily for 12 weeks does not reduce triglyceride levels in people with hypertriglyceridemia when compared with placebo. However, vitamin B6 appears to decrease total cholesterol and high-density lipoprotein (HDL) cholesterol by approximately 9% in these patients (59028).
• Infertility. Although there is interest in using oral vitamin B6 for infertility, there is insufficient reliable information about the clinical effects of vitamin B6 for this condition.
• Insomnia. Oral vitamin B6 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Clinical research in healthy adults with self-reported sleep difficulty shows that taking a specific product (LZ Complex3, Sanofi Consumer Healthcare Pty Ltd.) containing vitamin B6, zizyphus extract, hops extract, hydrolyzed milk protein (Lactium), and magnesium oxide nightly, 30 minutes before bed, for 2 weeks does not improve sleep quality, daytime functioning, or physical fatigue when compared with placebo. However, due to the large improvement seen in both the treatment and placebo groups, the effectiveness of this product is unclear (95971).
• Isoniazid-induced neuropathy. It is unclear if oral vitamin B6 prevents the development of neuropathy in patients taking isoniazid. Details: Preliminary clinical research in patients taking isoniazid for tuberculosis shows that taking vitamin B6 (pyridoxine) 6 mg daily reduces the development of neuropathy when compared with control (83068).
• Lactation. It is unclear if oral vitamin B6 helps to suppress postpartum lactation. Details: A meta-analysis of two small clinical trials shows that taking vitamin B6 (pyridoxine) 400-600 mg daily for 6-7 days postpartum does not suppress lactation when compared with no treatment (83047).
• Levetiracetam-induced side effects. While some conflicting evidence exists, several small, low-quality studies suggest that oral vitamin B6 (pyridoxine) may reduce some neuropsychiatric adverse effects related to the use of levetiracetam. Details: In an analysis of case reports, retrospective studies, and a single low-quality prospective study, improvement in levetiracetam-associated neuropsychiatric symptoms occurred in approximately 73% of patients taking pyridoxine (107137). A more recent preliminary clinical trial in children ages 1-17 years shows that taking pyridoxine 10 or 15 mg/kg daily as needed based on symptoms improves behavioral side effects associated with levetiracetam by a small amount when compared with low-dose pyridoxine 0.5 mg/kg daily used as placebo (107124). Also, observational research in children ages 9 months to 14 years has found that taking vitamin B6 is associated with improved behavior and a 44% lower risk of levetiracetam discontinuation when compared with no vitamin B6 supplementation (110455). Some observational research in adults with levetiracetam-associated irritability has found that taking vitamin B6 is associated with an improvement in irritability in 45% of patients when compared to baseline (107129). However, a small clinical trial in adults with epilepsy shows that taking pyridoxine 40 mg daily for 3 weeks does not improve levetiracetam-related psychiatric adverse effects when compared with placebo (110456). This study may have been underpowered to detect differences between groups. Pyridoxine doses used in the studies above have ranged from 50-400 mg daily in children and 40-600 mg daily in adults (107124,107129,107137,110456).
• Lung cancer. It is unclear if dietary or oral vitamin B6 reduces lung cancer risk. Details: Epidemiological research has found that higher serum levels of vitamin B6 in male smokers is associated with a lower risk of lung cancer (9454). Also, people with blood levels of vitamin B6 in the top quartile have a modestly lower risk of lung cancer when compared with those whose levels are in the lowest quartile. The association is stronger for males and for people who have smoked (97999). However, other epidemiological research found that increased dietary intake of vitamin B6 is not associated with a reduced risk of lung cancer (96164).
• Menopausal symptoms. Although there is interest in using oral vitamin B6 for menopausal symptoms, there is insufficient reliable information about the clinical effects of vitamin B6 for this condition.
• Motion sickness. Although there is interest in using oral vitamin B6 for motion sickness, there is insufficient reliable information about the clinical effects of vitamin B6 for this condition.
• Nausea and vomiting. It is unclear if oral vitamin B6 is beneficial for nausea and vomiting in patients using oral contraceptives. Details: An observational longitudinal study in healthy females taking oral contraceptives containing ethinyl estradiol and levonorgestrel has found that taking vitamin B6 25 mg daily for 6-12 months is associated with a 43% reduced risk of nausea when compared with no supplementation (90789).
• Nonalcoholic fatty liver disease (NAFLD). It is unclear if oral vitamin B6 for patients with NAFLD. Details: A small clinical trial in patients with NAFLD shows that taking vitamin B6 (pyridoxine) 30 mg three times daily for 12 weeks does not reduce levels of liver transaminases or plasma lipids when compared with baseline. However, hepatic fat accumulation was modestly reduced (107130). The validity of this study is limited by the lack of a comparator group.
• Obesity. It is unclear if oral vitamin B6 in beneficial in overweight or obese individuals. Details: A small clinical trial in females with a body mass index (BMI) of at least 25 kg/m² shows that taking vitamin B6 as pyridoxine 80 mg daily for 8 weeks reduces fat mass and improves insulin resistance and triglyceride levels by a small amount when compared with placebo. Although some other anthropometric and metabolic indices were improved when compared with baseline, there was no effect of pyridoxine on body weight, visceral adiposity, or other endpoints when compared with placebo (107131).
• Overall mortality. It is unclear if oral vitamin B6 reduces the risk of overall mortality. Details: Observational research in US adults has found that dietary intake of vitamin B6 in the highest quintile is associated with a 12% to 21% lower risk of all-cause mortality and a 31% to 44% lower risk of cardiovascular mortality when compared with the lowest quintile of dietary vitamin B6 intake (110451).
• Pancreatic cancer. It is unclear if oral vitamin B6 reduces the risk of pancreatic cancer. Details: Observational research has found that higher dietary intake of vitamin B6 is associated with a 37% lower risk of developing pancreatic cancer when compared with lower intake (104927).
• Postpartum depression. It is unclear if oral vitamin B6 is beneficial in patients with postpartum depression. Details: Preliminary clinical research in individuals considered at increased risk for postpartum depression, but without clinical depression, shows that taking vitamin B6 80 mg daily from the 28th week of pregnancy until birth, and then 40 mg daily for one month, reduces symptoms of depression 1.5 months after birth when compared with baseline (measured during the third trimester) and when compared with placebo. However, it is unclear if any of the patients included in the study developed postpartum depression, as there were no changes in overall symptoms in patients taking placebo (107126).
• Restless legs syndrome (RLS). It is unclear if oral vitamin B6 is beneficial in patients with RLS. Details: A small clinical study in adults with RLS who are beginning treatment with pramipexole shows that also taking vitamin B6 40 mg daily for 2 months moderately improves RLS scores and sleep quality scores when compared with pramipexole and placebo (110052).
• Schizophrenia. It is unclear if oral vitamin B6 is beneficial for patients with treatment-resistant schizophrenia. Details: Clinical research in male patients with treatment-resistant schizophrenia who are on a consistent antipsychotic dose shows that adding vitamin B6 300 mg twice daily for 16 weeks modestly improves psychotic symptoms and some measures of cognitive performance when compared with adding aripiprazole 5 mg twice daily (107128). More research is needed to determine if these benefits are clinically relevant.
• Seizures. It is unclear if oral vitamin B6 is beneficial for preventing seizures in patients with glycosylphosphatidylinositol (GPI) deficiency. Details: Observational case series in a small number of children and young adults with GPI deficiency has found that taking vitamin B6 20-30 mg/kg daily for 3-12 months is associated with some reduction in seizure frequency in 9 of 13 patients. However, no patient reached seizure freedom (107125,107135). In one case series, treatment for 12 months was associated with modest developmental improvements in almost all patients (107135). The study patient populations were slightly different in terms of age and underlying genetic causes for GPI deficiency.
• Sickle cell disease. Oral vitamin B6 has only been evaluated in combination with other B vitamins; its effect when used alone is unclear. Details: Preliminary clinical research in adults with sickle cell disease shows that taking vitamin B6 4.2-6 mg, vitamin B12 4.2-6 mcg, and folic acid 700 mcg daily might lower homocysteine levels. However, it is unknown if this will reduce the risk of endothelial damage in these patients (9324).
• Stroke. It is unclear if oral vitamin B6, either alone or with other B vitamins, is beneficial for stroke prevention. Details: There is some debate about whether supplementation with homocysteine-lowering B vitamins, including vitamin B6, can reduce the risk of stroke. A number of clinical studies and meta-analyses show that supplementation with folic acid, vitamin B6, and vitamin B12, alone or in combination, does not reduce the risk of stroke in patients with cardiovascular disease (CVD) or impaired kidney function (11387,13482,50423,83050,96150). However, a more recent meta-analysis of 10 clinical trials, including over 44,000 patients at risk for or with a history of CVD, shows that B vitamin supplementation reduces the relative risk of stroke by 10% when compared with placebo (97619). This meta-analysis differed from some of the earlier analyses due to the inclusion of several additional clinical trials. Also, another meta-analysis of three clinical trials including 9900 patients with a history of stroke shows that B vitamin supplementation reduces the relative risk of stroke recurrence by 13% when compared with placebo, although this finding was determined to have a low level of certainty. Based on two clinical trials, there was also a 17% reduced risk of vascular death and an 11% reduction in the combined risk of stroke, myocardial infarction, and vascular death (107136). In 2001, prior to the publication of the highest quality research on this topic, the US Food and Drug Administration (FDA) allowed a qualified health claim stating that, as part of a well-balanced diet that is low in saturated fat and cholesterol, folic acid, vitamin B6, and vitamin B12 may reduce the risk of vascular disease (102368). Unfortunately, even after the publication of higher quality research, it is still unclear which specific combination of B vitamins is optimal and which patients are most likely to benefit. One network meta-analysis shows that a combination of folic acid and vitamin B6 lowers the risk of stroke more effectively than B vitamin mixtures that include vitamin B12 (96165). However, this analysis is limited because it didn't account for dosing. Exposure to low, but not high amounts, of vitamin B12 (cyanocobalamin) seems to reduce stroke risk (96150).
• Tardive dyskinesia. It is unclear if oral vitamin B6 prevents tardive dyskinesia in patients taking neuroleptic drugs. Details: A small clinical study in patients taking neuroleptic drugs for schizophrenia shows that taking vitamin B6 (form not specified) 400 mg daily seems to improve Parkinsonian, dystonic, and dyskinetic symptoms when compared with placebo (8558).
• Tourette syndrome. Oral vitamin B6 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: A small, nonblinded clinical study in children aged 4-17 years with untreated Tourette syndrome or with chronic tic disorder and associated symptoms of anxiety shows that taking a liquid nutritional supplement providing vitamin B6 2.8 mg and L-theanine 200 mg daily for 2 months improves scores on the Yale Global Tic Severity Scale, but does not reduce anxiety, when compared with patients receiving psychoeducation (108555). This study may have been inadequately powered to detect a difference between groups.
• Vincristine-induced neuropathy. Oral vitamin B6 has only been evaluated in combination with pyridostigmine; its effect when used alone is unclear. Details: A small clinical study in children ages 11 months to 13 years with neuropathy due to vincristine treatment for acute lymphoblastic leukemia, shows that taking vitamin B6 150 mg/m2 and pyridostigmine 3 mg/kg twice daily for 3 months is associated with reduced severity of sensory and motor neuropathy when compared with baseline (104928). The validity of this finding is limited by the lack of a control group. More evidence is needed to rate vitamin B6 for these uses.

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LIKELY SAFE ...when niacin is taken in food or as a supplement in amounts below the tolerable upper intake level (UL) of 30 mg daily for adults 18 years of age and 35 mg daily for adults 19 years and older (6243). ...when prescription products are used orally and appropriately in doses of up to 2 grams daily (12033). CHILDREN:

LIKELY SAFE ...when used orally in amounts that do not exceed the tolerable upper intake level (UL). The ULs of niacin for children are: 1-3 years of age, 10 mg daily; 4-8 years of age, 15 mg daily; 9-13 years of age, 20 mg daily; 14-18 years of age, 30 mg daily (6243).

PREGNANCY AND LACTATION: LIKELY SAFE
when used orally in amounts that do not exceed the tolerable upper intake level (UL). The UL of niacin during pregnancy and lactation is 30 mg daily for 14-18 years of age and 35 mg daily for 19 years and older (6243). There is insufficient reliable information available about the safety of larger oral doses of niacin during pregnancy or lactation; avoid using.

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LIKELY SAFE ...when prescription products are used orally and appropriately (12033). ...when niacinamide supplements are taken orally in doses below the tolerable upper intake level (UL) set by the Institute of Medicine (IOM). The UL of niacinamide is 30 mg daily for adults 18 years of age and 35 mg daily for adults 19 years and older (6243).

POSSIBLY SAFE ...when used orally in doses greater than 30 mg but less than 900 mg daily. The European Food Safety Authority has set the tolerable upper intake level (UL) of niacinamide at 900 mg daily (104937). However, oral niacinamide has been safely used in doses up to 1500 mg daily for 12 weeks in some clinical trials (25561,94188,98940,107709,110502). ...when used topically and appropriately for up to 12 weeks (5940,93360,110498,110501).

CHILDREN: LIKELY SAFE
when used orally and appropriately. Niacinamide has been safely used in children for up to 7 years in doses below the tolerable upper intake level (UL) (4874,9957). The UL of niacinamide for children by age is: 1-3 years, 10 mg daily; 4-8 years, 15 mg daily; 9-13 years, 20 mg daily; 14-18 years, 30 mg daily (6243).

PREGNANCY AND LACTATION: LIKELY SAFE
when used orally in amounts that do not exceed the tolerable upper intake level (UL) for niacinamide. The UL of niacinamide during pregnancy and lactation is 30 mg daily for those 14-18 years of age and 35 mg daily for those 19 years and older (6243). There is insufficient reliable information available about the safety of larger oral doses of niacinamide or topical niacinamide; avoid using.

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LIKELY SAFE ...when used orally and appropriately in doses that do not exceed the tolerable upper intake level (UL) of 100 mg daily for adults (15). ...when used parenterally and appropriately. Injectable vitamin B6 (pyridoxine) is an FDA-approved prescription product (15).

POSSIBLY SAFE ...when used orally and appropriately in doses of 101-200 mg daily (6243,8558).

POSSIBLY UNSAFE ...when used orally in doses at or above 500 mg daily. High doses, especially those exceeding 1000 mg daily or total doses of 1000 grams or more, pose the most risk. However, neuropathy can occur with lower daily or total doses (6243,8195). ...when used intramuscularly in high doses and frequency due to potential for rhabdomyolysis (90795).

CHILDREN: LIKELY SAFE
when used orally and appropriately (3094).

CHILDREN: POSSIBLY SAFE
when used orally and appropriately in amounts exceeding the recommended dietary allowance (5049,8579,107124,107125,107135).

CHILDREN: POSSIBLY UNSAFE
when used orally in excessive doses, long-term (3094).

PREGNANCY: LIKELY SAFE
when used orally and appropriately. A special sustained-release product providing vitamin B6 (pyridoxine) 75 mg daily is FDA-approved for use in pregnancy. Vitamin B6 (pyridoxine) is also considered a first-line treatment for nausea and vomiting in pregnancy by the American College of Obstetrics and Gynecology (111601). However, it should not be used long-term or without medical supervision and close monitoring.

PREGNANCY: POSSIBLY UNSAFE
when used orally in excessive doses. There is some concern that high-dose maternal vitamin B6 (pyridoxine) can cause neonatal seizures (4609,6397,8197).

LACTATION: LIKELY SAFE
when used orally in doses not exceeding the recommended dietary allowance (RDA) (3094). The RDA in lactating women is 2 mg daily. There is insufficient reliable information available about the safety of vitamin B6 when used in higher doses in breast-feeding women.

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ALCOHOL (Ethanol) Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Probable •  Level of Evidence = D Concomitant use of alcohol and niacin might increase the risk of flushing and hepatotoxicity.  Details Alcohol can exacerbate the flushing and pruritus associated with niacin (4458,11689). Large doses of niacin might also exacerbate liver dysfunction associated with chronic alcohol use. A case report describes delirium and lactic acidosis in a patient taking niacin 3 grams daily who ingested 1 liter of wine (14510). Advise patients to avoid large amounts of alcohol while taking niacin.

ALLOPURINOL (Zyloprim) Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Probable •  Level of Evidence = C Theoretically, niacin might antagonize the therapeutic effects of uricosurics such as allopurinol.  Details Large doses of niacin can reduce urinary excretion of uric acid, potentially resulting in hyperuricemia (4860,4863,12033). Doses of uricosurics such as allopurinol might need to be increased to maintain control of gout in patients who start taking niacin (4458). People who have frequent attacks of gout despite uricosuric therapy should avoid niacin (4863).

ANTICOAGULANT/ANTIPLATELET DRUGS Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = D Theoretically, niacin may have additive effects when used with anticoagulant or antiplatelet drugs.  Details Several cases of clotting factor synthesis deficiency and coagulopathy have been reported in patients taking sustained-release niacin (25915). Also, thrombocytopenia has been reported in patients treated with niacin or niacin plus lovastatin (25916).

ANTIDIABETES DRUGS Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Probable •  Level of Evidence = B Niacin can increase blood glucose levels and may diminish the effects of antidiabetes drugs.  Details Niacin impairs glucose tolerance in a dose-dependent manner, probably by causing or aggravating insulin resistance and increasing hepatic production of glucose (4860,4863,11692,11693). In diabetes patients, niacin 4.5 grams daily for 5 weeks can increase plasma glucose by an average of 16% and glycated hemoglobin (HbA1c) by 21% (4860). However, lower doses of 1.5 grams daily or less appear to have minimal effects on blood glucose (12033). In some patients, glucose levels increase when niacin is started, but then return to baseline when a stable dose is reached (12033,93344). Up to 35% of patients with diabetes may need adjustments in hypoglycemic therapy when niacin is added (4458,4860,4863,11689,12033).

ANTIHYPERTENSIVE DRUGS Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = B Theoretically, niacin may increase the risk of hypotension when used with antihypertensive drugs.  Details The vasodilating effects of niacin can cause hypotension (4863,12033,93341). Furthermore, some clinical evidence suggests that a one-hour infusion of niacin can reduce systolic, diastolic, and mean blood pressure in hypertensive patients. This effect is not observed in normotensive patients (25917).

ASPIRIN Interaction Rating = Minor Be watchful with this combination. Severity = Insignificant •  Occurrence = Likely •  Level of Evidence = B Large doses of aspirin might alter the clearance of niacin.  Details Aspirin is often used with niacin to reduce niacin-induced flushing (4458,11689). Doses of 80-975 mg aspirin have been used, but 325 mg appears to be optimal (4458,4852,4853,11689). Aspirin also seems to reduce the clearance of niacin by competing for glycine conjugation. Taking aspirin 1 gram seems to reduce niacin clearance by 45% (14524). This is probably a dose-related effect and not clinically significant with the more common aspirin dose of 325 mg (11689,14524).

BILE ACID SEQUESTRANTS Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = D Bile acid sequestrants can bind niacin and decrease absorption. Separate administration by 4-6 hours to avoid an interaction.  Details In vitro studies show that colestipol (Colestid) binds about 98% of available niacin and cholestyramine (Questran) binds 10% to 30% (14511).

GEMFIBROZIL (Lopid) Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = D Theoretically, concomitant use of niacin and gemfibrozil might increase the risk of myopathy in some patients.  Details A case of myopathy from concomitant use of niacin and gemfibrozil has been reported (25920). Niacin alone has also been associated with cases of myopathy (26100,26111). Using gemfibrozil with niacin might further increase the risk of developing myopathy.

HEPATOTOXIC DRUGS Interaction Rating = Moderate Be cautious with this combination. Severity = High •  Occurrence = Possible •  Level of Evidence = D Theoretically, concomitant use of niacin and hepatotoxic drugs might increase the risk of hepatotoxicity.  Details Niacin has been associated with cases of liver toxicity, especially when used in pharmacologic doses (4863,11689,11691,25929,25930,25931). Sustained-release niacin preparations appear to be associated with a higher risk of hepatotoxicity than immediate-release niacin (11691,25930,25931,93342).

HMG-CoA REDUCTASE INHIBITORS ("Statins") Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = D Theoretically, concomitant use of niacin and statins might increase the risk of myopathy and rhabdomyolysis in some patients.  Details Some case reports have raised concerns that niacin might increase the risk of myopathy and rhabdomyolysis when combined with statins (14508,25918). However, a significantly increased risk of myopathy has not been demonstrated in clinical trials, including those using an FDA-approved combination of lovastatin and niacin (Advicor) (7388,11689,12033,14509).

PROBENECID (Benemid) Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Probable •  Level of Evidence = C Theoretically, niacin might antagonize the therapeutic effects of uricosurics such as probenecid.  Details Large doses of niacin reduce urinary excretion of uric acid, potentially causing hyperuricemia (4863,12033). Doses of uricosurics such as probenecid might need to be increased to maintain control of gout in patients who start taking niacin (4458). People who have frequent attacks of gout despite uricosuric therapy should avoid niacin (4863).

SULFINPYRAZONE (Anturane) Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Probable •  Level of Evidence = C Theoretically, niacin might antagonize the therapeutic effects of uricosurics such as sulfinpyrazone.  Details Large doses of niacin reduce urinary excretion of uric acid, potentially causing hyperuricemia (4863,12033). Doses of uricosurics such as sulfinpyrazone might need to be increased to maintain control of gout in patients who start taking niacin (4458). People who have frequent attacks of gout despite uricosuric therapy should avoid niacin (4863).

THYROID HORMONE Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Probable •  Level of Evidence = D Theoretically, niacin might antagonize the therapeutic effects of thyroid hormones.  Details Clinical research and case reports suggests that taking niacin can reduce serum levels of thyroxine-binding globulin by up to 25% and moderately reduce levels of thyroxine (T4) (25916,25925,25926,25928). Patients taking thyroid hormone for hypothyroidism might need dose adjustments when using niacin.

TRANSDERMAL NICOTINE (Nicoderm) Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = D Theoretically, concomitant use of niacin and transdermal nicotine might increase the risk of flushing and dizziness.  Details Niacin and nicotine can both cause flushing and dizziness (496,96211).

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ANTICOAGULANT/ANTIPLATELET DRUGS Interaction Rating = Moderate Be cautious with this combination. Severity = High •  Occurrence = Unlikely •  Level of Evidence = D Theoretically, niacinamide may have additive effects when used with anticoagulant or antiplatelet drugs, especially in patients on hemodialysis.  Details Several cases of thrombocytopenia have been reported for hemodialysis patients treated with niacinamide 1 gram daily. Hemodialysis patients receiving niacinamide had almost a three-fold higher risk of developing thrombocytopenia when compared with those receiving placebo (25563,98940).

CARBAMAZEPINE (Tegretol) Interaction Rating = Moderate Be cautious with this combination. Severity = High •  Occurrence = Possible •  Level of Evidence = D Niacinamide might increase the levels and adverse effects of carbamazepine.  Details Plasma levels of carbamazepine were increased in two children given high-dose niacinamide, 60-80 mg/kg/day. This might be due to inhibition of the cytochrome P450 enzymes involved in carbamazepine metabolism (14506). There is not enough data to determine the clinical significance of this interaction.

PRIMIDONE (Mysoline) Interaction Rating = Moderate Be cautious with this combination. Severity = High •  Occurrence = Possible •  Level of Evidence = D Niacinamide might increase the levels and adverse effects of primidone.  Details Case reports in children suggest niacinamide 60-100 mg/kg/day reduces hepatic metabolism of primidone to phenobarbital, and reduces the overall clearance rate of primidone (14506); however, there is not enough data to determine the clinical significance of this potential interaction.

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AMIODARONE (Cordarone) Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = B Theoretically, vitamin B6 might increase the photosensitivity caused by amiodarone.  Details Despite initial case reports suggesting that pyridoxine may have a protective effect against amiodarone-induced photosensitivity, preliminary clinical research suggests that pyridoxine may actually exacerbate this adverse effect (8892,8893).

ANTIHYPERTENSIVE DRUGS Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = B Theoretically, vitamin B6 may have additive effects when used with antihypertensive drugs.  Details Research in hypertensive rats shows that vitamin B6 can decrease systolic blood pressure (30859,82959,83093). Similarly, clinical research in patients with hypertension shows that taking high doses of vitamin B6 may reduce systolic and diastolic blood pressure, possibly by reducing plasma levels of epinephrine and norepinephrine (83091).

LEVODOPA Interaction Rating = Minor Be watchful with this combination. Severity = Moderate •  Occurrence = Unlikely •  Level of Evidence = D Vitamin B6 may increase the metabolism of levodopa when taken alone, but not when taken in conjunction with carbidopa.  Details Vitamin B6 (pyridoxine) enhances the metabolism of levodopa, reducing its clinical effects. However, this interaction does not occur when carbidopa is used concurrently with levodopa (Sinemet). Therefore, it is not likely to be a problem in most people (3046).

PHENOBARBITAL (Luminal) Interaction Rating = Moderate Be cautious with this combination. Severity = High •  Occurrence = Possible •  Level of Evidence = D High doses of vitamin B6 may reduce the levels and clinical effects of phenobarbital.  Details Preliminary clinical evidence suggests that vitamin B6 200 mg daily can reduce plasma levels of phenobarbital, possibly by increasing metabolism. It is not known whether lower doses have any effect. Advise people taking phenobarbital to avoid high doses of vitamin B6 (3046,10801).

PHENYTOIN (Dilantin) Interaction Rating = Moderate Be cautious with this combination. Severity = High •  Occurrence = Possible •  Level of Evidence = D High doses of vitamin B6 may reduce the levels and clinical effects of phenytoin.  Details Preliminary clinical evidence suggests that vitamin B6 200 mg daily can reduce plasma levels of phenytoin, possibly by increasing metabolism. It is not known whether lower doses have any effect. Advise people taking phenytoin to avoid high doses of vitamin B6 (3046,10801).

(Read more about VITAMIN B6)

General ...Orally, niacin is well tolerated in the amounts found in foods. It is also generally well tolerated in prescription doses when monitored by a healthcare provider.
Most Common Adverse Effects:
Orally: Flushing, gastrointestinal complaints (abdominal pain, constipation, diarrhea, heartburn, nausea, vomiting), and elevated liver enzymes.
Serious Adverse Effects (Rare):
Orally: Hepatotoxicity, myopathy, thrombocytopenia, and vision changes.

Cardiovascular ...Orally, flushing is a common dose-related adverse reaction to niacin. A large meta-analysis of clinical studies shows that up to 70% of patients may experience flushing (96211). Although flushing can occur with doses of niacin as low as 30 mg daily, it is more common with the larger doses used for treatment of dyslipidemia. The flushing reaction is due to prostaglandin-induced blood vessel dilation and can also include symptoms of burning, tingling, urticaria, erythema, pain, and itching of the face, arms, and chest. There may also be increased intracranial blood flow and headache (4889,26089,93341,104933). Onset is highly variable and ranges from within 30 minutes to as long as 6 weeks after the initial dose (6243). Flushing can be minimized via various strategies, including taking doses with meals, slow dose titration, using extended release formulations, pretreating with non-steroidal anti-inflammatory drugs, taking regular-release niacin with meals, or taking the sustained-release product at bedtime (4852,4853,4854,4857,4858,25922,26073,26084). Flushing often diminishes with continued use but can recur when niacin is restarted after missed doses (4863,6243,26081). The vasodilating effects of niacin can also cause hypotension, dizziness, tachycardia, arrhythmias, syncope, and vasovagal attacks, especially in patients who are already taking antihypertensive drugs (4863,12033,93341,110494).
High doses of niacin can raise homocysteine levels. A 17% increase has been reported with 1 gram daily and a 55% increased has been reported with 3 grams daily. Elevated homocysteine levels are an independent risk factor for cardiovascular disease (490); however, the clinical significance of this effect is unknown. A large-scale study (AIM-HIGH) found that patients receiving extended-release niacin (Niaspan) 1500-2000 mg daily with a statin had an over two-fold increased risk of ischemic stroke (1.6%) when compared with those receiving only simvastatin (0.7%). However, when the risk was adjusted for confounding factors, niacin was not found to be associated with increased stroke risk (17627,93354). A meta-analysis of three clinical trials conducted in approximately 29,000 patients showed a higher risk of mortality in patients taking niacin in addition to a statin when compared with a statin alone. However, with a p-value of 0.05 and confidence interval including 1, the validity of this finding remains unclear (97308).

Endocrine ...Orally, niacin can impair glucose tolerance in a dose-dependent manner. Dosages of 3-4 grams daily appear to increase blood glucose in patients with or without diabetes, while dosages of 1.5 grams daily or less have minimal effects (12033). Niacin is thought to impair glucose tolerance by increasing insulin resistance or increasing hepatic output of glucose (4863,11692,11693). In patients with diabetes, niacin 4.5 grams daily for 5 weeks has been associated with an average 16% increase in plasma glucose and 21% increase in glycated hemoglobin (HbA1C) (4860). Up to 35% of patients with diabetes may need to increase the dose or number of hypoglycemic agents when niacin is started (4458,4860,4863,11689,12033). Occasionally, severe hyperglycemia requiring hospitalization can occur (11693). In patients with impaired fasting glucose levels, niacin may also increase fasting blood glucose, and adding colesevelam might attenuate this effect (93343).
Although patients without diabetes seem to only experience small and clinically insignificant increases in glucose (4458), niacin might increase their risk of developing diabetes. A meta-analysis of clinical research involving over 26,000 patients shows that using niacin over 5 years is associated with increased prevalence of new onset type 2 diabetes at a rate of 1 additional case of diabetes for every 43 patients treated with niacin (96207). This finding is limited because the individual trials were not designed to assess diabetes risk and the analysis could not be adjusted for confounding factors like obesity. One small clinical study shows that taking extended-release niacin with ezetimibe/simvastatin does not increase the risk of a new diagnosis of diabetes or need for antidiabetic medication when compared with ezetimibe/simvastatin alone after 16 months (93344). This may indicate that the increased risk of developing diabetes is associated with niacin use for more than 16 months.
Niacin therapy has also been linked with hypothyroidism and its associated alterations in thyroid hormone and binding globulin tests (such as decreased total serum thyroxine, increased triiodothyronine, decreased thyroxine-binding globulin levels, and increased triiodothyronine uptake) (25916,25925,25926,25928).

Gastrointestinal ...Orally, large doses of niacin can cause gastrointestinal disturbances including nausea, vomiting, bloating, heartburn, abdominal pain, anorexia, diarrhea, constipation, and activation of peptic ulcers (4458,4863,12033,26083,93341,96211). These effects may be reduced by taking the drug with meals or antacid, and usually disappear within two weeks of continued therapy (4851,26094). Gastrointestinal effects may be more common with time-release preparations of niacin (11691).

Hematologic ...Orally, sustained-release niacin has been associated with cases of reversible coagulopathy, mild eosinophilia, and decreased platelet counts (4818,25915,26097,93340). Also, there have been reports of patients who developed leukopenia while taking niacin for the treatment of hypercholesterolemia (25916).

Hepatic ...Orally, niacin is associated with elevated liver function tests and jaundice, especially with doses of 3 grams/day or more, and when doses are rapidly increased (4458,4863,6243). The risk of hepatotoxicity appears to be higher with slow-release and extended-release products (4855,4856,4863,6243,11691,12026,12033,93342). Niacin should be discontinued if liver function tests rise to three times the upper limit of normal (4863). There are rare cases of severe hepatotoxicity with fulminant hepatitis and encephalopathy due to niacin (4863,6243,11691). Also, there is at least one case of niacin-induced coagulopathy resulting from liver injury without liver enzyme changes (93340).

Musculoskeletal ...Orally, niacin has been associated with elevated creatine kinase levels (4818,4888). Also, several cases of niacin-induced myopathy have been reported (26100,26111). Concomitant administration of niacin and HMG-CoA reductase inhibitors may increase the risk of myopathy and rhabdomyolysis (14508,25918,26111); patients should be monitored closely.

Neurologic/CNS ...Orally, high-dose niacin has been associated with cases of neuropsychiatric adverse events such as extreme pain and psychosis. Two 65-year-old males taking niacin orally for 5 months for the treatment of dyslipidemias developed severe dental and gingival pain. The pain was relieved by the discontinuation of niacin. The pain was thought to be due to inflammation and pain referral to the teeth (4862). In one case report, a 52-year-old male with no history of psychiatric illness who initially complained of hot flushes when taking niacin 500 mg daily, presented with an acute psychotic episode involving mania after niacin was increased to 1000 mg daily (93350).

Ocular/Otic ...Orally, chronic use of large amounts of niacin has been associated with dry eyes, toxic amblyopia, blurred vision, eyelid swelling, eyelid discoloration, loss of eyebrows and eyelashes, proptosis, keratitis, macular edema, and cystic maculopathy, which appear to be dose-dependent and reversible (4863,6243,26112).

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General ...Orally, niacinamide is well tolerated in amounts typically found in food. When used topically and orally in higher doses, niacinamide seems to be generally well tolerated.
Most Common Adverse Effects:
Orally: Dizziness, drowsiness, itching, gastrointestinal disturbances, headache, and rash.
Topically: Burning sensation, itching, and mild dermatitis.

Dermatologic ...Orally, large doses of niacinamide are associated with occasional reports of rashes, itching, and acanthosis nigricans (4880,11695,11697,14504,107709). Topically, application of niacinamide in a cream has been reported to cause a burning sensation, itching and pruritus, crusting, and mild dermatitis (93357,93360,110501,110498).

Endocrine ...Orally, niacinamide in high doses, 50 mg/kg daily, has been associated with modestly higher insulin requirements in patients with type 1 diabetes, when compared with taking niacinamide 25 mg/kg daily. Theoretically, high-dose niacinamide might increase insulin resistance, although to a lesser extent than niacin (4881,14512).

Gastrointestinal ...Orally, large doses of niacinamide can cause gastrointestinal disturbances including nausea, vomiting, heartburn, anorexia, epigastric pain, flatulence, and diarrhea (6243,11694,11695,11696,11697,107709).

Hematologic ...Orally, niacinamide supplementation might increase the risk for thrombocytopenia in patients undergoing hemodialysis (98940,107709). A meta-analysis of small clinical studies shows that taking niacinamide during hemodialysis to reduce phosphate levels is associated with a 2.8-fold increased risk for thrombocytopenia when compared with placebo. In one of the included studies, platelet levels returned to normal within 20 days after niacinamide discontinuation (98940).

Hepatic ...Orally, older reports of elevated liver function tests with high doses of niacinamide (3 grams or more daily) have raised concerns about liver toxicity. However, newer studies have not reported this concern; it is possible that some of these cases were due to contamination with niacin (4880,11694,11695,14503).

Neurologic/CNS ...Orally, large doses of niacinamide can cause dizziness, drowsiness, and headaches (11694,11695,11696,11697,107709).

(Read more about NIACINAMIDE)

General ...Orally or by injection, vitamin B6 is well tolerated in doses less than 100 mg daily.
Most Common Adverse Effects:
Orally or by injection: Abdominal pain, allergic reactions, headache, heartburn, loss of appetite, nausea, somnolence, vomiting.
Serious Adverse Effects (Rare):
Orally or by injection: Sensory neuropathy (high doses).

Dermatologic ...Orally, vitamin B6 (pyridoxine) has been linked to reports of skin and other allergic reactions and photosensitivity (8195,9479,90375). High-dose vitamin B6 (80 mg daily as pyridoxine) and vitamin B12 (20 mcg daily) have been associated with cases of rosacea fulminans characterized by intense erythema with nodules, papules, and pustules. Symptoms may persist for up to 4 months after the supplement is stopped, and may require treatment with systemic corticosteroids and topical therapy (10998).

Gastrointestinal ...Orally or by injection, vitamin B6 (pyridoxine) can cause nausea, vomiting, heartburn, abdominal pain, mild diarrhea, and loss of appetite (8195,9479,16306,83064,83103,107124,107127,107135). In a clinical trial, one patient experienced infectious gastroenteritis that was deemed possibly related to taking vitamin B6 (pyridoxine) orally up to 20 mg/kg daily (90796). One small case-control study has raised concern that long-term dietary vitamin B6 intake in amounts ranging from 3.56-6.59 mg daily can increase the risk of ulcerative colitis (3350).

Hematologic ...Orally or by injection, vitamin B6 (pyridoxine) can cause decreased serum folic acid concentrations (8195,9479). One case of persistent bleeding of unknown origin has been reported in a clinical trial for a patient who used vitamin B6 (pyridoxine) 100 mg twice daily on days 16 to 35 of the menstrual cycle (83103). It is unclear if this effect was due to vitamin B6 intake.

Musculoskeletal ...Orally or by injection, vitamin B6 (pyridoxine) can cause breast soreness or enlargement (8195).

Neurologic/CNS ...Orally or by injection, vitamin B6 (pyridoxine) can cause headache, paresthesia, and somnolence (8195,9479,16306). Vitamin B6 (pyridoxine) can also cause sensory neuropathy, which is related to daily dose and duration of intake. Doses exceeding 1000 mg daily or total doses of 1000 grams or more pose the most risk, although neuropathy can occur with lower daily or total doses as well (8195). The mechanism of the neurotoxicity is unknown, but is thought to occur when the liver's capacity to phosphorylate pyridoxine via the active coenzyme pyridoxal phosphate is exceeded (8204). Some researchers recommend taking vitamin B6 as pyridoxal phosphate to avoid pyridoxine neuropathy, but its safety is unknown (8204). Vitamin B6 (pyridoxine) neuropathy is characterized by numbness and impairment of the sense of position and vibration of the distal limbs, and a gradual progressive sensory ataxia (8196,10439). The syndrome is usually reversible with discontinuation of pyridoxine at the first appearance of neurologic symptoms. Residual symptoms have been reported in patients taking more than 2 grams daily for extended periods (8195,8196). Tell patients daily doses of 100 mg or less are unlikely to cause problems (3094).

Oncologic ...In females, population research has found that a median intake of vitamin B6 1. 63 mg daily is associated with a 3.6-fold increased risk of rectal cancer when compared with a median intake of 1.05 mg daily (83024). A post-hoc subgroup analysis of results from clinical research in adults with a history of recent stroke or ischemic attack suggests that taking folic acid, vitamin B12, and vitamin B6 does not increase cancer risk overall, although it was associated with an increased risk of cancer in patients who also had diabetes (90378). Also, in patients with nasopharyngeal carcinoma, population research has found that consuming at least 8.6 mg daily of supplemental vitamin B6 during treatment was associated with a lower overall survival rate over 5 years, as well as a reduced progression-free survival, when compared with non-users and those with intakes of up to 8.6 mg daily (107134).

(Read more about VITAMIN B6)